A variety of parallel optical communications modules exist for simultaneously transmitting and/or receiving multiple optical data signals over multiple respective optical data channels. Parallel optical transmitter modules have multiple optical transmit channels for simultaneously transmitting multiple optical data signals over multiple respective optical waveguides (e.g., optical fibers). Parallel optical receiver modules have multiple optical receive channels for simultaneously receiving multiple respective optical data signals over multiple respective optical waveguides. Parallel optical transceiver modules have multiple optical transmit channels and multiple optical receive channels for simultaneously transmitting and receiving multiple optical data signals over multiple respective transmit and receive optical waveguides. Bidirectional (BiDi) parallel optical transceiver modules have multiple BiDi channels for simultaneously transmitting and receiving optical data signals over each channel.
For each of these different types of parallel optical communications modules, a variety of designs and configurations exist. A typical layout for a parallel optical communications module includes a housing and a circuit board, such as a printed circuit board (PCB), disposed inside of the housing. Various electrical components and optoelectronic components (i.e., laser diodes and/or photodiodes) are mounted on the circuit board. Such mounting arrangements are often referred to as chip-on-board (COB) mounting arrangements.
In a typical COB mounting arrangement, a plurality of laser diodes, a plurality of photodiodes, a laser diode driver integrated circuit (IC), a receiver IC, and various other electrical components are mounted on and electrically interconnected with the circuit board. Parallel optical transmitter and transceiver modules typically also include a plurality of monitor photodiodes for monitoring the optical output power levels of the laser diodes. The laser diode driver IC adjusts the modulation and/or bias currents of the laser diodes based on the monitored optical output power levels.
Laser diodes are very sensitive to temperature. Generally, in order to increase the speed of laser diodes without sacrificing reliability, the operating temperatures of the laser diodes need to be kept at or below some maximum allowable temperature. Photodiodes are also sensitive to temperature, but generally not as sensitive as laser diodes. Heat dissipation solutions for optical communications modules are designed to prevent the temperatures of the laser diodes and photodiodes from rising above maximum allowable temperatures. For example, for high speed performance, it may be necessary to maintain the temperature of the laser diodes at or below 80° Celsius (C), and in some cases, at or below 70° C.
The laser diodes, receive photodiodes and monitor photodiodes are often arranged in respective arrays formed in respective semiconductor chips. These chips are typically mounted on a metal heat sink pad of the circuit board, which in many cases is the electrical ground plane of the circuit board. Heat generated by the chips is dissipated into the heat sink pad. Air flow through the housing is often used to assist in heat dissipation. In these types of heat dissipation systems, the temperatures of the laser diodes can rise above 80° C., particularly when the laser diodes are in their active power states. Such high temperatures can lead to poor performance and can shorten the life expectancies of the laser diodes. A need exists for a heat dissipation solution that is effective at maintaining the temperatures of active elements such as laser diodes and photodiodes at or below maximum allowable temperatures, particularly in parallel optical communications module that have a plurality of laser diodes and photodiodes that generate a large amount of heat.
Another common component of a typical parallel optical communications module is the optical subassembly (OSA). The OSA optically couples light between the ends of optical waveguides (e.g., optical fibers) and the laser diodes and photodiodes of the module. OSAs that are used in parallel optical communications modules typically include one or more rows of optical elements (e.g., collimating lenses) that couple light between the ends of the respective optical waveguides and the module. Along each of the associated optical pathways, the OSA typically includes additional optical elements, such as total internal reflection (TIR) lenses, for example, for operating on the light beams propagating along the respective pathways. For example, in COB mounting solutions of the type described above, the OSA commonly employs TIR surfaces along the optical pathways for turning the optical pathways by 90° relative to the optical axes of the optical fibers.
As the number of channels of parallel optical communications modules and the number of fibers increase, the number of rows of optical elements in the OSA that provide the optical interface between the ends of the optical fibers and the module also increases. This increase in the number of rows of optical elements in the OSAs can lead to an increase in the height of the optical communications module, which can lead to an increase in overall system size, reduced module mounting density and an increase in system costs. A need exists for an OSA that can accommodate a large fiber count while also having a low profile.